rightly so

adverb1

1. •
   In a manner that is factual or just; correctly, fairly, justly, truly; also, in a manner acceptable or excusable in the circumstances; understandably.

   • His name is hight Pollente, rightly so / For that he is so puissant and strong, / That vvith his povvre he all doth ouergo, / And makes them subiect to his mighty vvrong; […] — 1596